1. Field of the Invention
This invention relates to an electrographic recording material adapted for use in electrographic printing processes and to a method of making and using such an electrographic recording material. More particularly, it relates to an electrographic recording material comprising a vinyl ester interpolymer latex in the electrically insulating layer.
2. Description of the Prior Art
In general electrographic recording processes involve forming a latent image upon an electrically insulating charge-retentive layer of an electrographic recording material by impressing an electric charge corresponding to an original pattern and treating or developing the latent image by applying to the charge-retentive layer a colored resinous powder or toner which clings to the charged areas but which does not adhere to the uncharged areas. The developed image is then fixed by application of heat and/or pressure to the electrographic recording material to fuse the toner particles to the charge-retentive layer and form a permanent visible image. The electrographic recording material comprises an electroconductive sheet support coated with the electrically insulating charge-retentive layer comprising an electrically insulating polymeric binder and optionally a pigment or filler. The sheet support is generally paper which has been treated with ionic salts or polymers to provide electroconductivity.
Vinyl acetate interpolymers have been widely used as the electrically insulating polymeric binder of the dielectric or electrically insulating charge-retentive layer of electrographic recording material. In the preparation of such electrographic recording material, the vinyl acetate interpolymers are usually applied from organic solvent solution. As a means of reducing solvent emissions, acid modified vinyl acetate interpolymers have been applied in aqueous ammoniacal solution. However the viscosity of such solutions has limited the application to low concentrations of interpolymer and the consequent need to drive off large amounts of water has created a process of manufacture with a very low energy efficiency. Attempts to increase the interpolymer concentration and reduce the viscosity problem have been made by means of latex interpolymers of vinyl acetate. In conventional latex polymerization, rather large quantities of emulsifier and protective colloid are required and as a result, dielectric coatings prepared from vinyl acetate interpolymer latices have exhibited poor charge retention especially under humid conditions and have given electrographic images of extremely low density.